This invention relates generally to semiconductor sheets, and more specifically to methods and apparatus for manufacturing semiconductor wafers.
Wafers formed of semiconductor materials are used in a variety of applications and most, if not all, such applications require an increasing number of such wafers. For example, the use of photovoltaic systems has become more common and of greater importance in the production of energy. Moreover, the use of photovoltaic systems is therefore expected to increase dramatically. At least some known photovoltaic systems use a semiconductor substrate, such as a substrate consisting of single crystal or poly-crystalline silicon. However, the use of photovoltaic technology may be limited by the cost of semiconductor wafers used in the photovoltaic systems.
A wide variety of fabrication methods exist for producing semiconductor wafers. In at least one known fabrication method, poly-crystalline silicon wafers for use in solar cells are produced by melting a high-purity material in an inert atmosphere. In such a method, the resulting silicon melt is cooled to form a polycrystalline ingot which is then sliced with a wire saw or an inner diameter blade to produce wafers of a desired thickness and size.
Other known fabrication methods of producing wafers rely on a random nucleation of crystals in the semiconductor material melt. Such methods generally produce low-cost wafers, but because control of the nucleation of the semiconductor material melt is difficult, such wafers are generally of a low quality. Use of low-quality wafers within photovoltaic cells generally lowers the efficiency of such cells. Moreover, because the control of the nucleation of the semiconductor material is difficult, the costs of manufacturing such wafers is generally higher than with other fabrication methods.